use super::super::var::*;
use super::*;

/// An [Axis Variations Table](
/// https://docs.microsoft.com/en-us/typography/opentype/spec/avar).
#[derive(Clone, Copy, Debug)]
pub struct Table<'a> {
	/// The segment maps array — one segment map for each axis
	/// in the order of axes specified in the `fvar` table.
	pub segment_maps: SegmentMaps<'a>,
}

impl<'a> Table<'a> {
	/// Parses a table from raw data.
	pub fn parse(data: &'a [u8]) -> Option<Self> {
		let mut s = Stream::new(data);

		let version = s.read::<u32>()?;
		if version != 0x00010000 {
			return None;
		}

		s.skip::<u16>(); // reserved
		Some(Self {
			segment_maps: SegmentMaps {
				// TODO: check that `axisCount` is the same as in `fvar`?
				count: s.read::<u16>()?,
				data: s.tail()?,
			},
		})
	}

	/// Maps a single coordinate
	pub fn map_coordinate(&self, coordinates: &mut [NormalizedCoordinate], coordinate_index: usize) -> Option<()> {
		if usize::from(self.segment_maps.count) != coordinates.len() {
			return None;
		}

		if let Some((map, coord)) = self.segment_maps.into_iter().zip(coordinates).nth(coordinate_index) {
			*coord = NormalizedCoordinate::from(map_value(&map, coord.0)?);
		}

		Some(())
	}
}

/// An axis value map.
#[derive(Clone, Copy, Debug)]
pub struct AxisValueMap {
	/// A normalized coordinate value obtained using default normalization.
	pub from_coordinate: i16,
	/// The modified, normalized coordinate value.
	pub to_coordinate: i16,
}

impl FromData for AxisValueMap {
	const SIZE: usize = 4;

	#[inline]
	fn parse(data: &[u8]) -> Option<Self> {
		let mut s = Stream::new(data);
		Some(AxisValueMap {
			from_coordinate: s.read::<i16>()?,
			to_coordinate: s.read::<i16>()?,
		})
	}
}

/// A list of segment maps.
///
/// Can be empty.
///
/// The internal data layout is not designed for random access,
/// therefore we're not providing the `get()` method and only an iterator.
#[derive(Clone, Copy)]
pub struct SegmentMaps<'a> {
	count: u16,
	data: &'a [u8],
}

impl<'a> SegmentMaps<'a> {
	/// Returns the number of segments.
	pub fn len(&self) -> u16 {
		self.count
	}

	/// Checks if there are any segments.
	pub fn is_empty(&self) -> bool {
		self.count == 0
	}
}

impl core::fmt::Debug for SegmentMaps<'_> {
	fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
		write!(f, "SegmentMaps {{ ... }}")
	}
}

impl<'a> IntoIterator for SegmentMaps<'a> {
	type Item = LazyArray16<'a, AxisValueMap>;
	type IntoIter = SegmentMapsIter<'a>;

	#[inline]
	fn into_iter(self) -> Self::IntoIter {
		SegmentMapsIter {
			stream: Stream::new(self.data),
		}
	}
}

/// An iterator over maps.
#[allow(missing_debug_implementations)]
pub struct SegmentMapsIter<'a> {
	stream: Stream<'a>,
}

impl<'a> Iterator for SegmentMapsIter<'a> {
	type Item = LazyArray16<'a, AxisValueMap>;

	fn next(&mut self) -> Option<Self::Item> {
		let count = self.stream.read::<u16>()?;
		self.stream.read_array16::<AxisValueMap>(count)
	}
}

fn map_value(map: &LazyArray16<AxisValueMap>, value: i16) -> Option<i16> {
	// This code is based on harfbuzz implementation.

	if map.is_empty() {
		return Some(value);
	} else if map.len() == 1 {
		let record = map.get(0)?;
		return Some(value - record.from_coordinate + record.to_coordinate);
	}

	let record_0 = map.get(0)?;
	if value <= record_0.from_coordinate {
		return Some(value - record_0.from_coordinate + record_0.to_coordinate);
	}

	let mut i = 1;
	while i < map.len() && value > map.get(i)?.from_coordinate {
		i += 1;
	}

	if i == map.len() {
		i -= 1;
	}

	let record_curr = map.get(i)?;
	let curr_from = record_curr.from_coordinate;
	let curr_to = record_curr.to_coordinate;
	if value >= curr_from {
		return Some(value - curr_from + curr_to);
	}

	let record_prev = map.get(i - 1)?;
	let prev_from = record_prev.from_coordinate;
	let prev_to = record_prev.to_coordinate;
	if prev_from == curr_from {
		return Some(prev_to);
	}

	let curr_from = i32::from(curr_from);
	let curr_to = i32::from(curr_to);
	let prev_from = i32::from(prev_from);
	let prev_to = i32::from(prev_to);

	let denom = curr_from - prev_from;
	let k = (curr_to - prev_to) * (i32::from(value) - prev_from) + denom / 2;
	let value = prev_to + k / denom;
	i16::try_from(value).ok()
}
